a8 = a1 + 7d
d = (a8 - a1)/7
d = 19-5/7
d = 2
<span>4x -x² =0</span>
<span>x(4-x)=0</span>
<span>x=0 или 4-x=0</span>
<span> -x=-4</span>
<span> x=4</span>